text: #include "libm.h"
  
  #if LDBL_MANT_DIG == 53 && LDBL_MAX_EXP == 1024
  long double atanhl(long double x) { return atanh(x); }
  #elif (LDBL_MANT_DIG == 64 || LDBL_MANT_DIG == 113) && LDBL_MAX_EXP == 16384
  /* atanh(x) = log((1+x)/(1-x))/2 = log1p(2x/(1-x))/2 ~= x + x^3/3 + o(x^5) */
  long double atanhl(long double x)
  {
      union ldshape u = {x};
      unsigned e = u.i.se & 0x7fff;
      unsigned s = u.i.se >> 15;
  
      /* |x| */
      u.i.se = e;
      x = u.f;
  
      if (e < 0x3ff - 1) {
          if (e < 0x3ff - LDBL_MANT_DIG / 2) {
              /* handle underflow */
              if (e == 0)
                  FORCE_EVAL((float)x);
          } else {
              /* |x| < 0.5, up to 1.7ulp error */
              x = 0.5 * log1pl(2 * x + 2 * x * x / (1 - x));
          }
      } else {
          /* avoid overflow */
          x = 0.5 * log1pl(2 * (x / (1 - x)));
      }
      return s ? -x : x;
  }
  #endif
  